Overload protective means



Dec. 30, 1941. L. s. WALLE 2,268,229

OVERLOAD PROTECTIVE MEANS Filed DEC. 12, 1939 Fig.1.

' &\\\\\\ Inventor": Ludwig 5. Walls,

His Attorneytransformer.

Patented Dec. 30, 1941 OVERLOAD PROTECTIVE MEANS Ludwig S. Walle,Lansdowne, Pa., assignor to REISSUED General Electric Company, acorporation of New York JU Application December 12, 1939, Serial No.308,785 (Cl. 200-116) 10 Claims.

My invention relates to overload protective means, more particularly toprotective devices for electric energy translating apparatus of the oilimmersed type such as transformers, and has for its object a simple,reliable and inexpensive protective device of this type.

My invention is especially useful in distribution transformers which aremounted in convenient but isolated positions in the distribution networkand are inspected at infrequent intervals.

In carrying out my invention, I provide a protective device consistingof a thermally operable snap acting switching means which is connectedin the secondary circuit of the transformer and immersed in thetransformer oil so as to be responsive to the oil temperature. I alsoprovide a latching means for holding the switching means in its opencircuit position after it has opened and closed a plurality of timeswithin a predetermined range. This latching means is operated by asecond temperature responsive means in response to the current in thesecondary circuit or to the oil in which it is immersed so as to movethe latching means to hold the switch in its open circuit position. Ialso provide manually operated means operable from the exterior of thetransformer casing for opening and closing the switching means.

For a more complete understanding of my invention, reference should behad to the accompanying drawing showing a protective device embodying myinvention applied to a transformer,

while Fig. 2 is a front elevation view of the bimetallic snap'operatingmeans.

Referring to the drawing, I have provided.

overload protective means comprising in the form shown a; snap actionbimetallic thermostat II) which constitutes a bridging switching memberin the circuit of the secondary winding II of a This thermostat has asubstantially rectangular body portion which is support ed at its centeron a pin or post l2 secured to an insulating support I3 made of asuitable electrically insulating'n iaterial such as slate.

The main rectangular portion of the thermostat has a 'concavo-convexform for the purpose of giving it a snap action. When the thermostat isin position to close the secondary circuit of the secondary winding II,as shown in the drawing,

the, side of the thermostat adjacent the support I! is concave. Upon anincrease in temperature of the thermostat to a predetermined value, theunequal expansion of its two metals, the metal having the greatercoefiicient of expansion being adjacent the support I3, causes it tosnap at some predetermined temperature to reverse its shape as indicatedby the dotted line position I. The side of the thermostat adjacent thesupport 13 is then convex. When the temperature of the thermostat dropsto a predetermined point, the thermostat resumes the shape indicated inthe drawing with a snap action.

As shown, the rectangular portion of the thermostat is provided at itsopposite ends with central extensions I5 and Hi to which are securedelectric switch contacts |5a and lid respectively. These contactscooperate with stationary contacts l1 and I8 secured to the support l3.Preferably, as shown, the stationary contacts are mounted on bolts orlugs which extend through the base and are clamped to the base by meansof suitable nuts. form connection nection of the thermostat winding H, r

The extension l6 extends downward below the contact 5a and is benttoward the right-hand as seen in Fig. l of the drawing to form alatching projection 2|. This projection 2| engages a latching member 22made of electrically insulating material after the thermostat ID hasopened and closed the circuit a number of times within a predeterminedrange whereby the ther- The opposite ends of the bolts terminals l9 and20 for conprotective device including the mostat is held in the opencircuit position.

The projection 22 is operated by a second bimetallic thermostat 23 to alatching position and, as shown, is mounted on the movable end of thisthermostat. The opposite end of the thermostat is secured rigidly and ingood heat conducting relation therewith to the bolt or post 24 formingthe support for the stationary contact l8. To facilitate a good thermalcontact, the post may be made in two parts secured together by a screwconnection 25 so as to clamp the end of the thermostat 23 between thetwo parts.

Moreover, the bolt or post 24 has an electrical resistance such that ithas substantially the same thermal characteristics as the transformersecondary winding II and primary winding 26. In other words, heat isgenerated in the bolt 24 by the current passing through it at such ratethat the temperature rise of the bolt follows the temperature rise, andalso temperature decrease, of the transformer windings. Preferably, topromote this temperature rise in the bolt, it is sur-- rounded by a heatinsulating jacket 24a made of a suitable heat and electricallyinsulating material such as fiber. This heat insulating jacket in incircuit with the secondary prevents the rapid cooling of the bolt by thesurrounding oil 21 in the transformer.

This heat generated in the bolt 24 raises its temperature above thetemperature of the surrounding oil and the heat is transferred byconduction to the thermostat 23. Also the oil itself, particularly onlight over-currents, is heated by the windings and approximates thetemperature of the windings. The oil will also have some effeet on theheating of the thermostat 23. As the temperature of the thermostat 23rises, its distortion moves the insulating latch 22 upward, as seen inFig. 1, until finally the latch is in a position to engage theprojection 2| and prevent the return snap action of the thermostat Illto its closed circuit position, shown in the drawing. During the timethat the thermostat 23 is being heated, the thermostat ID will have beenheated to snap to its open position and then cooled to snap to itsclosed position, several times.

In the operation of the transformer, the secondary current flowingthrough the thermostat l heats the thermostat. Also heat is imparted tothe thermostat by the cooling fiuid, shown as the oil 21 in which thetwo thermostats and the transformer windings are immersed. Upon theoccurrence of a substantial overload current in the secondary windingthe thermostat I0 is heated to a temperature causing it to snap to thereverse position indicated by dotted lines and thereby open thesecondary circuit. It is contemplated that the temperature of thethermostat under such conditions will be considerably above thetemperature of the oil in which it is immersed. Consequently, thethermostat is cooled rapidly by the oil and snaps to reclose the circuitafter remaining in its open circuit position a short interval such as afew seconds.

This overload current, however, likewise heats the thermostat 23although the response of the thermostat 23 is slower, it being heated aspreviously noted at a rate approximately the rate of heating of thetransformer windings. Its temperature, however, is somewhat higher withsubstantial overloads than the temperature of the surrounding oil. Whenthe thermostat It has opened and closed the circuit a number of times,such as five or more, the thermostat 23 will have moved the projection23 to a latching position in which it holds the thermostat ill in itsopen circuit position.

Of course the rate at which the thermostats are heated will depend uponthe current in the secondary winding. The thermostat l0 will be adjustedor constructed ordinarily to open and close the circuit a number oftimes in response to an overload current of a predetermined high valueby the time it is latched open by the second thermostat. In the event ofa suddenly applied overhead resulting in a current considerably greaterthan this predetermined current value, the thermostats will be heated atcorrespondingly increased rates, but will be cooled quickly because ofthe lower temperature of the transformer oil. As a result, thethermostat ill will have approm'mately the same number of opening andclosing operations as with the predetermined current value.

The plurality of reclosing operations provides for the resumption ofservice in the event that the excessively heavy load is removed duringthe opening and closing circuit interval. If the heavy overloadpersists, then the circuit is permanently latched open.

Moreover the thermostat It is constructed and arranged to remain open inresponse to a predetermined temperature which is the maximum permissibletemperature of the oil. This temperature is not high enough to cause thethermostat to snap open, but it is high enough to cause it to remainopen after it has snapped open, 1. e., high enough to prevent reclosureof the thermostat. In theevent that the oil reaches this temperaturebecause of continued light overloads the thermostat it] remains openuntil the oil cools regardless of whether it is secured open by thelatch 22. Preferably this maximum oil temperature is not high enough,however, to cause the thermostat 23 to move the latch into an engagingposition. It will thus be observed that during these persistentpredetermined light overloads the thermostat ill opens and closes thecircuit an indefinite number of times, remaining open for relativelylong time intervals, and is not finally latched open by the thermostat23. The arcs generated by the opening of the circuit heat the oil andcontribute in the raising of the oil temperature to the maximum value.

I have also provided manual means for bodily moving the thermostat Illto its open and closed positions. This consists of an arm 28 inside thetransformer tank 29 having its free end opposite th inner end of a rod33 carrying the thermostat Ill. The upper end of the arm 28 is pivotedon a shaft 3! which extends through the wall of the tank and has securedto it an exterior operating arm 32. On the endof the arm 32 is a link 33through which the hook of an operating pole may be inserted to move thearm 32 downward and open the circuit. It is contemplated that the weightof the operating pole on th arm 32 will be sufilcient to hold thethermostat ill in its open circuit position.

As shown, the rod 30 extends through an aperture provided for it in thebase l3, the post l2 constituting a flange secured to the rod 33, andalso through an aperture in the thermostat it. The left-hand end of therod 3E3 is threaded and provided with an adjustment nut 35 bearing on ahelical spring 35 which, in turn, presses against a collar 36 on the rod33. This collar engages the thermostat Hi and holds it against theflange [2, or in a predetermined adjusted relation. with the fiange l2.A second spring 371 surrounding the opposite end of the rod 36 biasesthe rod in a right-hand direction. It will be understood that thesprings 35 and 3i are strong enough to maintain the desired contactpressure and overpower substantially the thermostat ill.

When the latch 22 engages the projection 2i, the thermostat i3 is heldin its open circuit position regardless of the temperature to which itsubsequently cools. The release of the thermostat lil from the latch 22is a manual operation whereby the thermostat ill is moved bodily towardthe left. It is carried out by pulling downward on the lever 32 to movethereby the supporting rod 38 and the thermostat it toward the left, asseen in the drawing, far enough to disengage the projection Zl from thelatch. This manual release operation has of course the prerequisite thatthe thermostat it has cooled to such a temperature that it is trying tosnap to its closed position and the thermostat 23 has cooled to such atemperature that it is trying to move the latch 22 downward to aposition out of the path of the projection 2 l While I have shown aparticular embodiment of my invention, it will be understood, of course,that I do not wish to be limited thereto, since many modifications maybe made and I, therefore, contemplate by the appended claims to coverany such modifications as fall within the true spirit and scope of myinvention.

What I claim as new and desire to secure by Letters Patent in the UnitedStates is:

1. A protective device for a translating device immersed in oilcomprising a bimetallic thermostat arranged to snap from one position toanother in response to changes in temperature thereof, said thermostatbeing arranged to be immersed in the oil' with the translating device soas to be responsive to the temperature of the oil, circuit control meansactuated by said thermostat, said circuit control means being connectedin a circuit of the translating device and being normally in a closedcircuit position, connections for heating said thermostat in response tothe current in said circuit, a second thermostat, latching meansactuated by said second thermostat in response to a predeterminedtemperature of said second thermostat for holding said said firstthermostat in its open circuit position, and means for manually movingsaid first thermostat to release it from said latching means.

2. A protective device comprising temperature responsive operating meansarranged to move from one position to another position and back to saidone position in response to changes in temperature thereof, circuitcontrol means actuated by said operating means between closed and opencircuit positions, said circuit control means being normally in a closedcircuit posi tion, connections for heating said operating means inresponse to the current in said control means, a second temperatureresponsive operating means, means actuated by said second operatingmeans when heated to a predetermined temperature to hold said firstoperating means in its open circuit position, and connections forheating said second operating means in response to the current in saidcontrol means, said first operating means being heated to its operatingtemperature before said second operating means is heated to itsoperating temperature so that said first operating means operates saidcircuit control means a plurality of times before said second operatingmeans moves said holding means to hold said first operating means in itsopen circuit position,

3. A protective device comprising a bimetallic thermostat arranged tosnap from one position to another in response to changes in temperaturethereof, circuit control means actuated by said thermostat betweenclosed and open circuit positions, said circuit control means beingnormally in a closed circuit position, connections for heating saidthermostat in response to the current in said control means, a secondthermostat, stop means actuated by said second thermostat when heated toa predetermined temperature to hold said first thermostat in its opencircuit position, and connections for heating said second thermostat inresponse to the current in said control means, said first thermostatbeing heated to its operating temperature before said second thermostatis' heated to its operating temperature so that said first thermostatoperates said circuit control means a plurality of times before saidsecond thermostat moves said stop means to hold said first thermostat inits open circuit position.

4. A protective device comprising a pair of stationary contacts, meansfor connecting said contacts in circuit with an energy translatingdevice, a bimetallic thermostat provided with spaced movable contactsengaging said stationary contacts to close a circuit through saidthermostat, said thermostat being heated by the current passing throughit and arranged when heated to a predetermined temperature to snap toanother position and thereby move said movable contacts to open saidcircuit, a second thermostat having one end movable in response tochanges in temperature, a latching member carried by the movable end ofsaid second thermostat, means for heating said second thermostat inresponse to the current in said circuit at a rate substantially the sameas the rate of heating of the translating device whereby said secondthermostat moves said latching member in response to a predeterminedmaximum temperature to a position to hold said first thermostat in itsopen circuit position, said first thermostat being heated to itsoperating temperature before said second thermostat is heated to itsoperating temperature, and said first thermostat operating to open andclose the circuit a plurality of times before said second thermostatmoves said latching member to a position to hold said first thermostatin its open circuit position, and manually operated means for mostatbodily to open said circuit.

5. A protective device for an electric ranslating device immersed in acooling fluid, said device being arranged to be immersed in the coolingfluid with the translating device, comprising switching means arrangedto be connected in a circuit of the translating device, temperatureresponsive operating means connected to said switching means so as toopen and close said switching means in response to changes in thetemperature of the cooling fluid and arranged to maintain said switchingmeans in a closed circuit position when the temperature of saidoperating means is below a predetermined temperature and to move saidswitching means to an open circuit position when the temperature of saidoperating means is above said predetermined temperature, connections forheating said operating means in response to the current in a circuit ofthe translating device, and means for manually moving said temperatureresponsive means to open and close said switching means.

6. A protective device for an electric translating device immersed inoil, said device being arranged to be immersed in the oil with thetranslating device, comprising switching means arranged to be connectedin a circuit of the translating device, temperature responsive operatingmeans connected to said switching means so as to open and close saidswitching means in response to changes in the temperature of the oil andarranged to maintain said switching means in a closed circuit positionwhen the temperature of said operating means is below a predeterminedtemperature and to move said switching means to an open circuit positionwhen the temperature of said operating means is above said predeterminedtemperature, connections for heating said operating means in response tothe current in a circuit of the translating device, a second temperatureresponsive operating means, means actuated by said second operatingmeans in response to a predetermined temperature for holding said firstoperating means in its open circuit moving said first therposition, andconnections for heating said second operating means in response to thecurrent in circuit of the translating device.

' '7. A protective device for an electric translating device immersed inoil, said device being arranged to be immersed in the oil with thetranslating device, comprising switching means arranged to be connectedin a circuit of the translating device, temperature responsive operatingmeans connected to said switching means so as to open and close saidswitching means in response to changes in the temperature of the oil andarranged to maintain said switching means in a closed circuit positionwhen the temperature of said operating means is below a predeterminedtemperature and to move said switching means to an open circuit positionwhen the temperature of said operating means is above said predeterminedtemperature, connections for heating said operating means in response tothe current in a circuit of the translating device, temperatureresponsive latching means for holding said operating means in its opencircuit position, and manually operated means for releasing saidoperating means from said latching means.

8. A protective device for an electric translating device immersed in acooling fluid, said device being arranged to be immersed in the coolingfluid with the translating device, comprising a bimetallic thermostatarranged to snap from one position to another in response to changes inits temperature when immersed in the cooling fluid, circuit controlmeans arranged for connection in a circuit of the translating deviceactuated by said thermostat between closed and open circuit positions,said circuit control means being normally in a closed circuit position,connections for heating said thermostat in response to the current in acircuit of said translating device, a second thermostat, latch meansactuated by said second thermostat in response to a predeoil andarranged to maintain said switching means in a closed circuit positionwhen the temperature of said operating means is below a predeterminedtemperature and to move said switch ing means to an open circuitposition when the temperature of said operating means is above saidpredetermined temperature, connections for heating said operating meansin response to the current in the circuit of the translating device soas to cause said operating means to open and close said switching meansafter relatively short time intervals in response to a current in thecircuit of the translating device of a predetermined high value and toopen and close said switching means after relatively long time intervalsin response to a current in the circuit of the translating device of apredetermined low value, and a second temperature responsive operatingmeans for holding said first temperature responsive operating means inits open circuit position after a plurality of said short time intervaloperations.

10. A protective device for an electric translating device immersed in acooling fluid, said device being arranged to be immersed in the coolingfluid with the translating device, comprising switching means arrangedto be connected in a circuit of the translating device, temperatureresponsive operating means connected to said switching means so as toopen and close said switching means in response to changes in thetemperature of the cooling fluid and arranged to maintain said switchingmeansin a closed circuit position when the temperature of said operatingmeans is below a predetermined temperatureand to move said switchingmeans to an open circuit position when the temperature of said operatingmeans is above said pretermined operating temperature to hold said firstthermostat in its open circuit position, and connections for heatingsaid second thermostat in response to the current in a circuit of saidtranslating device, said first thermostat being heated to its operatingtemperature to open said circuit control means before said secondthermostat is heated to its predetermined operating temperature so thatsaid first thermostat operates to open and close said circuit controlmeans a plurality of times before said second thermostat moves saidlatch means to hold said first thermostat in its open circuit position.

9. A protective device for an electric translating device immersed inoil, said device being arranged to be immersed in the oil with thetranslating device, comprising switching means arranged to be connectedin a circuit of the translating device, temperature responsive operatingmeans connected to said switching means so as to open and close saidswitching means in response to changes in the temperature of thedetermined temperature, connections for heating said operating means inresponse to the current in the circuit of the translating device so asto cause said operating means to open and close said switching meansafter relatively short time intervals in response to a current in thecircuit of the translating device of a predetermined high value and toopen and close said switching means after relatively long time intervalsin response to a current in the circuit of the translating device of apredetermined low value, a second temperature responsive Operating meansarranged to be immersed in the cooling fiuid with the translatingdevice, a latch operable by said second operating means to a position tohold said first temperature responsive operating means in its opencircuit position, and means for heating said second temperatureresponsive operating means in response to the current in a circuit ofthe translating device to cause said second operating means to move saidlatch to said latching position after a plurality of said short timeinterval operations of said first operating means.

LUDWIG S. WALLE.

